1. Field
The present disclosure relates to a porous Nafion membrane and a method for preparing the same very easily through a one-step process. The porous Nafion membrane may be used in various industrial fields, such as fuel cells, gas separators, electrolytic cells, redox flow batteries, humidifiers and sensors, and a method for preparing the same.
2. Description of the Related Art
Fuel cells are power generating systems that may produce electric energy through an electrochemical reaction of hydrogen as a fuel and oxygen as an oxidant. Such fuel cells may be classified into various types, including polymer electrolyte membrane fuel cells (PEMFC) and direct methanol fuel cells (DMFC), based on driving temperature, or the like.
Fuel cells use an electrolyte membrane. The electrolyte membrane is made of a polymer material having proton conductivity, and serves not only as a channel through which protons generated by the oxidation at an anode move toward a cathode but also as an insulating membrane by which the anode and cathode are separated electrically from each other.
A typical example of currently available electrolyte membranes is a sulfonated tetrafluoroethylene membrane, i.e., NAFION® electrolyte membrane, available from Dupont Co. Meanwhile, such a Nafion electrolyte membrane may be also used in a humidified system.
A porous Nafion membrane may significantly improve a quality of a fuel cell and enhances a resistance against delamination of a membrane electrode.
The porous Nafion membrane may be prepared by a leaching process, extraction process, high-temperature process or a high-pressure process according to the related art. However, according to observations of the inventors, such processes for preparing a porous Nafion membrane are very complicated, have a difficulty in developing a uniform porous structure, and provide through-pores (e.g. see EP 1152380).
Meanwhile, the inventors of the present disclosure have suggested a method for preparing a Nafion membrane having a porous surface layer and a dense lower layer (US 20130323496).
The above-mentioned method, however, is limited to a preparation of a Nafion membrane having a porous layer only at the surface layer. With the method, it is not possible to form a monolithic porous structure throughout the bulk of the Nafion membrane including the lower part of the surface layer, because pores rise toward the surface during the evaporation of a solvent and no pores are formed in the part below the surface.